High efficiency magnetic focusing device for cathode-ray tubes



D. P. INGLE 2,694,782 HIGH EFFICIENCY MAGNETIC ECCUSING DEVICE ECR CATHODE-RAY TUBES Filed May 19, 1951 Nov. 16, 1954 United States Patent Office 2,694,782 Patented Nov. 16, 1954 HIGH EFFICIENCY MAGNETIC FOCUSING DEVICE FOR CATHODE-RAY TUBES Donald Paul Ingle, Defiance, Ohio, assignor to All Star Products, Inc., Defiance, Ohio, a corporation of Ohio Application May 19, 1951, Serial No. 227,221 4 Claims. (Cl. 313-75) My invention relates to an improved focusing device for a cathode ray tube characterized by eliicient utilization of the permanent magnets employed.

Magnetic focusing devices for cathode ray tubes possess advantages of no power consumption and simplicity. However. they do require magnets having high values of stored energy, which magnets are expensive and often unavailable.

In my copending patent application Serial No. 194,097, entitled Magnetic Focusing Device for Cathode Ray Tubes, filed November 4, 1950, and assigned to the same assignee as the present invention, I have disclosed a magnetic focusing device that efiiciently utilizes the magnets because the magnets are sandwiched between spaced annular plates that have a considerable space in the direction of the cathode ray beam, which spacing is maintained even in the inner peripheries of the plates. The resultant rather long magnetic field has proven to be particularly eflicient in utilizing the stored energy of the permanent magnets.

The present invention increases the magnetic field produced by the permanent magnets still further. Briey, l provide a sleeve of soft iron or similar magnetic material which is welded or otherwise attached to the inner periphery of one of the annular magnetic plates. This sleeve extends outboard of the plates, or the cage defined thereby. The resultant magnetic flux, which tends to be concentrated along the axis of the ray beam, is highly effective in focusing the ray beam.

The eflicient utilization of the permanent magnets accomplished by the present invention makes it possible to achieve a greater focusing action with magnets of prescribed stored energy or, alternatively, to achieve the focusing action of existing units with magnets of smaller size than has heretofore been possible.

It is therefore a general object of the present invention to provide an improved magnetic focusing device for a cathode ray tube characterized by efficient utilization of the magnets employed therein.

Another object of the present invention is to provide a magnetic focusing device which incorporates the advantages of existing high efficiency focusing devices but is even more efficient.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:

Figure 1 is a side elevati;onal view of a cathode ray tube with the focusing device of the present invention mounted thereon;

Figure 2 is a view in perspective of the focusing device of the present invention;

Figure 3 is a cross-sectional view through axis 3-3, Figure 2;

Figure 4 is a cross-sectional view through axis 44, Figure 3; and,

Figure 5 is a fragmentary cross-sectional view through axis 5-5, Figure 3.

Referring now to Figure 1, there is shown generally at T a cathode ray tube having a neck portion N, a bayonet plug-type base B, and a viewing screen S. This tube includes electron gun elements (not shown) which produce a cathode or electron ray beam originating near the junction of the neck N and base B and travelling to the viewing screen S where it produces a visible trace. When the cathode ray tube is in a television receiver, the ray beam is scanned or caused to travel over the viewing screen S by a sweep coil C which is energized by suitable sweep currents.

The focusing apparatus of the present invention is indicated generally at 10, Figure l, and is received on the neck N of the tube T on the base side of the sweep coil C, as shown. The details of this apparatus are shown in Figures 2 to 5. It is the function of this apparatus to cause the ray beam to strike the viewing screen S in a sharply defined spot.

Referring now to Figures 2 to 5, the focusing device consists of a pair of annular plates, 12 and 14, constructed of soft iron or similar magnetic material. A series of permanent magnets 16 is sandwiched between these plates to form a cage. The plates are securely anchored to the magnets by the non-magnetic anchor screws 18 which are threadedly received in the plate 12.

The'plates 12 and 14 define a longitudinal magnetic field at their inner pcripheries, the intensity of this field being determined by the strength of the magnets 16. The intensity of this field is also controlled by the sleeve 20 which is of magnetic material and slides over the plates 12 and 14 as shown. Sleeve 20 is moved over the cage defined by the plates 12 and 14 by the lead screw 22 which is mounted on the bracket 24 secured to the sleeve 20. This screw is received in the tube 26 mounted on and extending outboard of the plate 12 and, at titsouter end, the screw 22 threadedly receives the cap nu A spring 30 bottoms against the bracket 24 and the tube 26 to urge these parts in spaced relation. Thus as the cap nut 28 is rotated, the sleeve 2f) is adjustably shifted over the cage defined by plates 12 and 14 and the magnets 16. Since this sleeve is magnetic, this motion varies the leakage fiux which extends between the plates outboard of the cage and thereby alters the flux within the cage. Only the latter flux tends to focus the ray beam.

The annular plate 14 carries the centering plate 32, these plates being secured for limited relative movements by the rivets 34 which are received in elongated slots 36 as shown in Figures 3 and 4. A U-shaped socket ear 38 extends outwardly and upwardly from one edge of the centering plate 32 and receives the mating headed end of the control rod 40. The control rod 40 passes through a relatively snug opening 12a in the plate 12. As the control rod 40 is rocked, the plate 32 is shifted in relation to the plate 14 to vary the position of center of the ray beam so as to center the image on the screen S.

A fiber sleeve 31 is wrapped about the cage defined by the plates 12 and 14 and magnets 16 to form a centering surface upon which the sleeve 20 slides.

In accordance with the present invention a magnetic sleeve 42 is affixed to the plate 12 by welding or similar means. This sleeve is attached to the inner periphery of the plate 12 and extends outboard of plates 12 and 14. That is, the sleeve 42 extends in the direction away from the cage defined by the plates 12 and 14 and magnets 16.

Preferably the focusing unit is mounted on the neck of the tube T with the sleeve 42 extending towards the base of the tube.

The sleeve 42 substantially increases the focusing ability of the unit of Figure 2. It is believed that this increase is due primarily to the effect of the sleeve in increasing the relative proportion of the flux that is within the confines of the neck of the cathode ray tube as distinguished from outside the tube. This is believed to bc due to the effect of sleeve 42 in increasing the surface area of the inner periphery of plate 12 through which this liux passes. Since it is this flux that is effective in focusing, the ability of the unit to focus the ray beam is correspondingly increased. Moreover, the period of time the ray beam is subject to the magnetic field is increased by the presence of the sleeve 42.

In any event, I have found by actual experiment that focusing units constructed in accordance with the present invention display a substantially increased focusing ability as compared to units without the sleeve 42. This makes possible a more effective focusing with magnets of fixed size, or reduction in the size of the magnets to achieve the same focusing effect.

If desired, sleeve 31 may be affixed to the sleeve 20 to move in unison therewith.

While I have rshown and described the present invention as applied to a specific type of focusing unit, it will, of course, be understood that it is applicable to focusing units generally where a magnetic field is created by permanent magnets sandwiched between a pair of annular plates. lt will also be apparent that various modifications and alternative constructions can be made Without departing from the true spirit and scope of the present invention. I therefore intend by the appended claims to cover all such modifications and alternative constructions as fall within their true spirit and scope.

What l claim as new and desire to secure by Letters Patent of the United States is:

l. A magnetic focusing device for a cathode ray tube having a neck comprising in combination, a pair of magnetic annular plates adapted to receive the neck of the tube, a magnet sandwiched between said plates to create a magnetic field therebetween, a magnetic shunting sleeve encircling the annular plates and mounted for shifting movements relative thereto to control the intensity of said magnetic field, a magnetic centering disk shiftably mounted on one of the plates to center the cathode ray beam, and a fixed magnetic sleeve carried by the other of the plates at its inner periphery and extending solely in the outboard direction with respect to the plates to define flux paths between said sleeve and said other plate greater in length than the distance between the plates.

2. A magnetic focusing device for a cathode ray tube having a neck comprising in combination, a pair of magnetic annular plates adapted to receive the neck of the tube, a magnet sandwiched between said plates to create a magnetic field therebetween, a magnetic shunting sleeve encircling the annular plates and mounted for shifting movements relative thereto to control the intensity of said fixed magnetic field, and a magnetic sleeve carried by one of the plates at its inner periphery and extending .solely in the outboard direction with respect to the plates to dene flux paths between said sleeve and said other plate greater in length thanthe distance between the lates.

p 3. A magnetic focusing device for a cathode ray tube having a neck comprising in combination, a pair of magnetic annular plates adapted to receive the neck of the tube, a magnet sandwiched between said plates to create a magnetic field therebetween, a magnetic centering disk shiftably mounted on one of the plates to center the cathode ray beam, and a magnetic sleeve tixedly carried by the other of the plates at its inner periphery and extending solely in the outboard direction with respect to the plates to dene flux paths between said sleeve and said other plate greater in length than the distance between the plates.

4. A magnetic focusing device adapted for a cathode ray tube having a neck comprising in combination, a pair of magnetic annular plates adapted to receive the neck of the tube, a magnet sandwiched between said plates to create a magnetic field therebetween, and a Xed magnetic sleeve carried by one of the plates at its inner periphery and extending solely in the outboard direction with respect to the plates to define flux paths between said sleeve and said other plate greater in length than the distance between the plates.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,354,661 Berejkoft Aug. 1, 1944 2,416,687 Fry Mar. 4, 1947 2,418,487 Sproul Apr. 8, 1947 2,456,399 Gethrnann Dec. 14, 1948 2,533,687 Quam Dec. l2, 1950 2,568,668 Steers Sept. 18, 1951 2,580,606 Schiel et al Jan. 1, 1952 2,591,820 Jackson Apr. 8, 1952 2,608,665 Parker Aug. 26, 1952 

